Papers by Author: Sylvain Fréour

Abstract: This paper presents the results of experimental research to investigate blade material surface deterioration of wind turbines located in arid areas caused by sand particles impacts and the resulting influence on their energetic performance. Tests are conducted in the erosion sandblaster then in the wind tunnel for uncoated Glass Fiber/Polyester blade at various angles and durations impact. The magnitudes of aerodynamics forces on a Naca 4412 profile are determined experimentally. All profiles (AR=0.571) are tested in a wind tunnel at air speed of 10 m/s at Reynolds number 6.5 x 10⁵. The results show the behavioral differences detected for the specimens with T =160 s, T = 240 s and T = 340 s (when Ra increases) by comparing them with the smooth specimen (T = 0 s, Ra= 0.94). Force coefficients (C_L and C_D) show significant changes which leads to a decrease of the lift-to-drag ratio and therefore there will be a notable performance loss. This will be an acceptable threshold for the case where t = 160s.

Abstract: This work investigates, by diffraction methods, the morphological texture influence on the residual stress analysis in polycrystals having cubic or hexagonal symmetries. Different extreme crystallite morphologies (sphere, disc and fiber, with their principal axes aligned along common directions) were considered in the present study. In a second part, crystallographic textures were accounted for, also, enabling to reflect the combined effect of the simultaneous occurrence of morphological and crystallographic textures. A stronger influence of morphological texture than that of the crystallographic texture in terms of stresses was observed. The main purpose of this work is to make the best choice of lattice planes (hkl) used for residual stress analysis, in elasticity, depending on the morphological (and crystallographic) texture of the polycristal.

Abstract: The historical Eshelby-Kröner self-consistent model is only valid in the case when grains can be assumed similar to ellipsoids aligned preferentially along a same direction into the polycrystal. In this work, distributions of crystallites morphologies and geometrical orientations were accounted for, owing to the so-called generalized self-consistent model, in order to satisfy Hills averages principles. Different nonlinear ε_φψ-vs.-sin²ψ distributions were predicted in elasticity, even in the absence of crystallographic texture, in the case when several morphologies and geometrical orientations coexist within the same polycrystal.

Abstract: The mechanical response of the composite structure in T650-35/PMR-15 aged at different temperatures was studied numerically. The time-dependent internal stresses in the composite ply and its constituents were computed during the creep process. In order to predict the effective properties of PMR-15/T650-35 composite ply in the temperature range [250-350°, the time-dependent mechanical properties of PMR-15 matrix determined experimentally [, were considered. The mechanical properties of the fibers do not experience any change due to the aging process in such a temperature range [2, . In order to achieve the computations, the visco-elastic Eshelby Kröner self-consistent model was used.

Abstract: The present work aims to investigate the validity of Eshelby-Kröner self-consistent model [1] for thermoelastic behaviour, in the case of a material reinforced by inclusions randomly oriented in the ply plane. The model provides predictive information on the properties and multi-scale mechanical states experienced by the material, accounting for its constituents properties, but also their morphology. However, it cannot reliably account for multiple inclusion morphologies (shape and orientation) in the material [2, 3, 4]. A study of the two applicable formulations and their limits leads to suggest a mixed formulation as an acceptable compromise between those alternatives. The results of this original approach are also described in the case of a thermo-mechanical load.

Abstract: This paper deals with the cure of an in-plane isotropic carbon-polymer tooling material, with a complex microstructure [1]. The Mori-Tanaka (MT) and Eshelby-Kröner self-consistent (EKSC) models are used in order to achieve a two-steps scale transition procedure, relating the microscopic properties of the material to their macroscopic counterparts. This procedure enables estimating the multi-scale mechanical states experienced by the material, i.e. the local (microscopic) stresses due to thermal and chemical shrinkage of the resin, along a typical, macroscopic stress-free, cure process. The influence of the chosen scale transition model on both the calculated effective properties of the material and its local stress states, is investigated. These results are a first step for investigating the service life fatigue of the material, as well as its failure behaviour.

Abstract: The scope of this work is the determination of single-crystals elastic constants (SEC) from X-ray diffraction lattice strains measurements performed on multi-phase polycrystals submitted to mechanical load through a bending device. An explicit three scales inverse self-consistent model is developed in order to express the SEC of a cubic phase, embedded in a multi-phase polycrystal, as a function of its X-ray Elasticity Constants. Finally, it is applied to a two-phases (α+β) titanium based alloy (Ti-17), in order to estimate Ti-17 β-phase unknown SEC. The purpose of the present work is to account the proper microstructure of the material. In particular, the morphologic texture of Ti-17 a-phase, i.e. the relative disorientation of the needle-shaped grains constituting this phase, is considered owing to the so-called Generalized Self-Consistent model.